Resistance to shock damage is important with respect to any rigid disk storage device, but is a critical concern in smaller drives used in portable devices such as lap top computers. Larger disk drives are subject to occasional shock conditions whereas small drives incorporated in portable equipment are regularly exposed to impact forces that often exceed 1000 g's. The common practice to overcome possible damage when the drive is not in use is the provision of a ramp structure to displace and support the transducer carrying sliders away from the disk surface. Using the load/unload (L/UL) technique, a ramp supports the suspension to retain the slider out of contact with the disk surface. Upon receipt of a read or write command, the slider is loaded from the ramp to a near contact transducing relationship with the data surface of the rotating disk and when the drive is subsequently idle, the actuator causes the suspension to engage the ramp and unload or remove the slider from data transducing cooperation with the disk data surface. In those systems that seek to power down the disk drive when not in use to effect power saving, L/UL cycles are a frequent occurrence. However, the use of the L/UL technique presents its own characteristic problems. While a rigid disk magnetic disk drive is a device wherein the head or slider that carries the transducer is separated from the disk during operation by a film of air between the air bearing surface and the disk media surface, the thickness of the film of air between the slider and media has become so small that occasional contact may be expected. With the fly height of state of the art sliders no more than 2.5 microinches above the media surface, it will be appreciated that only a minuscule asperity on the disk surface, minute particulate particle, or slight pitch or roll of the slider will result in contact between slider and disk or impose a foreign object that damages both disk and the slider air bearing surfaces. With such near contact operation, the engagement of the suspension with the ramp as the slider is unloaded or the departure from ramp engagement as the slider is loaded present occasions wherein there is an increased likelihood of undesired contact. Further, with current densities of more than 4000 tracks per inch, linear densities over 130 thousand bits per inch and the necessary magnetic coating thickness measured in angstroms, very little scratching or abrasion of the media is sufficient to destroy data and create an error condition. Since at each disk surface the slider will load and unload at random angular positions about the disk surface, a distribution of errors will occur if the L/UL mechanism fails to load and or unload correctly. As a result of slider/disk contact, particularly during loading when the slider may engage the disk and unloading when the slider may also engage the disk surface, the slider comers are damaged and the disk is scratched. The level of damage depends upon the particular slider/air bearing design, disk material, loading speed, air bearing roll and pitch stiffness, and disk runout. During slider/disk contact particulates from both the damaged slider and the scratched disk may be generated. As the number of head/disk contacts increase, the air bearing performance deteriorates rapidly. All the ingredients for a catastrophic failure are present and no early warning system exists to alert the user to impending failure. In the event that the slider contacts the disk, and depending upon the severity of the contact, a slider imprint forms on the disk which can easily be seen with the aid of modest magnification. During subsequent loadings, the slider may encounter the imprint, causing additional contacts around the imprint area. This cumulative contact causes further deterioration of the slider and media.
Drives designed for use in portable equipment are expected to survive a million load/unload cycles without damage, thus the importance of failure anticipation. Current drives are expected to have hundreds of thousands of power on hours of service before mean time to failure. In practice the operation of the devices is taken for granted and the possibility of failure ignored. When the time arrives for replacement to avoid the loss of valuable data, it is important that the user have an awareness. This may occur after a long useful life or a shortened life, due for example to a portable device being subjected to shock or rough handling.